An enhanced radio frequency transmitter suitable for use in a nuclear magnetic resonance logging tool, may employ a power amplifier that comprises two pairs of switching amplifiers and a summation stage. The first pair of switching amplifiers together generate a first pair of pulse sequences having an adjustable phase difference, while the second pair of switching amplifiers generate a second pair of pulse sequences, each pulse sequence in the second pair being provided a fixed phase offset from a respective pulse sequence in the first pair. The summation stage forms a combined signal from the pulse sequences in both said first and second pairs. The fixed phase offset operates to at least partly cancel a higher harmonic of the pulse sequences from the combined signal, thereby reducing energy losses downstream from the transmitter.